New calamitic mesogens derived from a furan ring: Synthesis, characterization and study of their mesomorphic behavior

摘要

A new series of mesogens bearing furan moiety, 4-R(5-(4-nitrophenyl)furan-2-yl)methylene)amino]phenyl 4-alkoxybenzoate (Ca-k) was synthesized by different organic methodologies. These mesogens possess an alkoxy chain at one arm and a nitro group at the opposite arm in addition to various linkages (imine and ester). Their chemical structures have been identified by various essential characterization techniques: infrared spectroscopy (MR), H-1 and C-13 nuclear magnetic resonance (NMR), and electron ionization-mass spectrometer (El-MS). The thermal transition and optical behavior properties of the homologous series have been studied by differential scanning calorimetry (DSC) and a polarizing optical microscope (POM), respectively. The compounds of this series (C-a-C-k) displayed liquid crystalline phases, and all mesogens exhibited an enantiotropic nematic phase (N) in heating and cooling cycles except the compounds (C-d, C-e and C-f) which showed a monotropic nematic phase in the cooling cycle only. Additionally, the last member of this series (C-k) showed a smectic A (SmA) phase in addition to the nematic phase. The obtained results showed that the enantiotropic and monotropic mesogenic properties, in addition to the thermal stability of the mesophase for all mesogens, have been influenced thoroughly by increasing the number of carbon atoms in the terminal alkoxy tail and the nitro group on the other side. In addition to these results, these mesogens could be affected by other factors, such as polarity and polarizability of the linkages and other connected groups in the molecules. The liquid crystalline behaviors of the target compounds have been studied and discussed extensively and compared structurally in related literature. Published by Elsevier B.V.